The present invention relates to a light irradiation device or an exposure device, and more particularly, to an improvement on the light irradiation device having a filter unit which includes red, green and blue filters selectively switchable for forming a latent image corresponding to the selected color image on a photosensitive image recording medium.
One example of a conventional image recording apparatus is shown in FIG. 1. The image recording apparatus 50 includes a monochromatic laser printer 55 and a color copying machine 60 coupled to the printer 55. The laser printer 55 generally includes a polygon scanner, a chargeable photosensitive drum, developer unit, and a fixing unit etc. The polygon scanner forms an electrostatic latent image on the photosensitive drum, the image corresponding to an image of an original or an image of a specific color. A toner image is formed on the latent image zone on the drum, and the toner image is transferred onto a plain paper or an overhead projector sheet at the developer unit, and the transferred image is fixed at the fixing unit. The sheet carrying the output image is simply discharged. Alternatively, the image carrying sheet is delivered to the color copying machine 60 by way of a delivery path 51. In the latter case, the laser printer 55 produces mask members M which independently carry a red image, green image and blue image.
The color copying machine 60 has an upper inner portion in which a mask carrying unit having an endless belt 62 is provided. The endless belt 62 is circularly driven in a direction indicated by arrows in FIG. 1 on which the mask member M is electrostatically attracted. The endless belt 62 is formed of a transparent and dielectric material such as PET. The mask member M is subjected to positional alignment with an elongated image recording medium S passing through an exposure stand 71.
At a position above the endless belt 62, a light irradiation device 63 is provided which is movable between a home position H and an end position E in directions indicated by arrows X1 and X2. As shown in FIG. 2, the light irradiation device 63 has a hollow cylindrical rotary body 64 to which a red filter 65R, a green filter 65G and a blue filter 65B are fixed at equi-angular spacing. A light source 80 having a white light lamp 66 and parabolic reflector 67 is positioned inside the filters. The rotary body 64 has an outer peripheral surface formed with a gears (not shown) engageable with a pinion 68. Further, a rack 69 driven by a drive source (not shown) is meshedly engaged with the pinion 68. Therefore, in accordance with the movement of the rack 69, the rotary body 64 is rotated about its axis through the pinion 68 and the gear. Therefore, one of the red, green and blue filters can be positioned in confrontation with the light source 80. As a result, a specific one of the red, green and blue lights is emitted onto the endless belt 62. The light irradiation device is disclosed, for example, in a Japanese Patent Publication No. 57-57692.
Turning back to FIG. 1, the image recording medium such as a microcapsule sheet S is adapted to pass through a space defined between the transparent endless belt 62 and the exposure stand 71 in a direction X3, and is wound over a takeup roller 73 by way of a pressure developing unit 72. The microcapsule sheet S is coated with microcapsules encapsulating therein photo-curable resins and coloring agents of cyan, magenta and yellow photo-curable upon irradiation of red light, green light and blue light, respectively to restrain the color generation. For the exposure operation, the exposure stand 71 has an ascent position to bring into intimate contact with the mask member M carried on the endless belt 62. Therefore, a latent image is formed on the microcapsule sheet S. Another image recording medium such as a cut developer sheet D can be fed to the pressure developing unit 72 in a direction X4, where the developer sheet D is superposed with the latent image section of the microcapsule sheet S and these sheets are pressed together. Accordingly, a visible image is formed on the developer sheet D. Further, thermal fixing unit 74 is provided for fixing the visible image, and a discharge tray 75 is provided to receive the developer sheet D.
For the exposure operation, the printer 55 produces a first mask member MR on which a red color information of one original image is contained. The first or red mask member MR is fed to the endless belt 62 of the mask carrying unit, and is attracted thereto. The mask member MR is subjected to position adjustment to be set at a proper exposure position.
Then, the exposure stand 71 is elevated so that the mask member MR and the microcapsule sheet S are in intimate contact with each other between the exposure stand 71 and the endless belt 62. Thereafter, the light irradiating device 63 is moved in the X1 direction from its home position H to the end position E for the light scan during which red light is irradiated through the red filter 65R onto the microcapsule sheet through the red mask member MR. After the light scanning, the light irradiation device 63 is moved back to the home position H in the direction X2. During this return travel, the rotary member 64 is angularly rotated by a predetermined angle by the rack 69 and the pinion 68, so that the green filter 65G is positioned in confrontation with the light source 80, while the mask member MR is discharged to a mask receiving section (not shown). The same is true with respect to the light irradiations through the green filter 65G and the blue filter 65B, so that latent images are formed at three times on an identical portion of the microcapsule sheet.
Thus, an intended color latent image is formed on the microcapsule sheet S. Then, the exposure stand 71 is moved to its descent position, and the microcapsule sheet S is moved in the X3 direction. In synchronization with the movement of the microcapsule sheet S, the developer sheet D is fed in the direction X4 and the pressure developing operation is performed at the pressure developing unit 72. After the pressure developing operation, the microcapsule sheet S is wound over the takeup means 73 whereas the developer sheet D is fed to the fixing unit 74 and is discharged on to the discharge tray 75.
As described above, the filter change is made by the rotation of the rotary body 64 through the driving engagements of the rack 69, the pinion 68 and the gear of the rotary body. Here, the exact angular rotation amount may be slightly changed due to backlash or irregular meshing engagement between the rack 69 and the pinion 68. Accordingly, precise positional registration of the red, green and blue filters 65R, 65G, 65B may not be attained. In this connection, a filter position detection means is provided for detecting the angular position of the filter, and feed back control is made for the precise position registration with respect to the light source. As a result, overall cost may be increased.
Further, as shown in FIG. 2, in the conventional light irradiation device 63 having the tubular filter member and the light source positioned within the tubular member, a temperature within the tubular member may be excessively elevated, if the light source if of a heat releasable type such as a halogen lamp. To avoid this drawback, a cooling duct may be connected to the interior space of the tubular filter member for feeding cooling air thereinto so as to cool the color resolution filters.
Still however, if a power source is inadvertently shut off, the cooling air supply to the interior of the tubular filter member is stopped. In such a situation, the temperature within the tubular filter member cannot be promptly lowered, since the light source, the filter tube, and the reflector accumulate the heat therein. Due to the nonsupply of the cooling air, the temperature of the tubular filter member becomes elevated, and the inherent color resolution function of the filters may be degraded by the heat.